That politics is becoming basically tribal has been surprising to some, but this is really just a confirmation of what political life has been for most of history: a battle over who we are, what we stand for, and what we want to believe in. A series of academic studies (Democracy for Realists being the most prominent) has argued with the benefit of growing empirical data that people, even the better educated, don’t vote based on policy. The authors Christopher Achen and Larry Bartels make the case that the “most important factor in voters’ judgments [is] their social and psychological attachments to groups.” In other words, if the same person, with the same genetics and life experience but no political attachments, decides to become a Republican, he is likely to become more pro-life. If that person decides to become a Democrat, he is likely to become more pro-choice.